JPH0530818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to 2,6-naphthalene dicarboxylic acid (hereinafter referred to as 2,6-NDCA). 2,6-NDCA is a raw material for producing polyethylene 2,6-naphthalate, polyester, polyamide, etc., which are used to produce films and textile products with excellent heat resistance.

Prior art It is known that 2,6-NDCA is produced by air oxidizing 2,6-dialkylnaphthalene in glacial acetic acid at high temperature and pressure in the presence of a cobalt and manganese catalyst and a bromine catalyst. . However, aldehydes and ketones by-produced in the oxidation reaction, brominated derivatives of 2,6-NDCA, oxidized polymers, and colored substances are mixed into the produced 2,6-NDCA, so the resulting crude 2,6-NDCA - The purity of NDCA is usually about 95%.

When 2,6-NDCA containing such impurities is used as a raw material for producing polyethylene 2,6-naphthalate, polyester, polyamide, etc.,
The degree of polymerization of the polymer may decrease, or the physical properties such as heat resistance of films and fibers made from the polymer may decrease, or the quality may deteriorate due to discoloration.

Therefore, it has been conventionally required that the purity of 2,6-NDCA be as high as 99% or higher.

The following methods for producing and purifying 2,6-NDCA have been proposed.

Oxidizing 2,6-diisopropylnaphthalene or its oxidized intermediate with molecular oxygen in a solvent containing at least 50% by weight of an aliphatic monocarboxylic acid having 3 or less carbon atoms to produce 2,6-naphthalene dicarboxylic acid. In the method, the oxidation of 2,6-diisopropylnaphthalene or its oxidized intermediates comprises:
(i) A heavy metal consisting of cobalt and/or manganese and (ii) a catalyst consisting of bromine in the presence of at least 0.2 mol of heavy metal as a component of the catalyst per 1 mol of 2,6-diisopropylnaphthalene or its oxidized intermediate. A method for producing 2,6-naphthalene dicarboxylic acid comprising
89445).

2,6-diisopropylnaphthalene or its oxidized intermediate is oxidized with molecular oxygen in a solvent containing at least 50% by weight of an aliphatic monocarboxylic acid having 3 or less carbon atoms to produce 2,6-naphthalene dicarboxylic acid. In the manufacturing method, oxidation of 2,6-diisopropylnaphthalene or its oxidized intermediate,
(i) a heavy metal consisting of cobalt and/or manganese and (ii) a catalyst consisting of bromine in the presence of at least 1% by weight of the heavy metal that is a component of the catalyst, based on the aliphatic monocarboxylic acid having 3 or less carbon atoms. A method for producing 2,6-naphthalenedicarboxylic acid (Japanese Patent Application Laid-Open No. 89446/1989).

Dissolve crude 2,6-NDCA in an alkaline aqueous solution,
Heat treatment is performed by stirring at 100 to 250°C for 1 to 5 hours,
Then, after decolorizing with a solid adsorbent, acidic gas such as carbon dioxide or sulfur dioxide is injected to lower the pH and 2,6-NDCA is precipitated as a monoalkaline salt (Japanese Patent Publication No. 52-20993).

A method of treating an alkaline aqueous solution of crude 2,6-NDCA with an oxidizing agent such as an alkali perhalate or an alkali manganate, and then blowing carbon dioxide gas or sulfur dioxide gas to separate 2,6-NDCA as a monoalkali salt (special method) 1976-68554).

After catalytically hydrogenating an alkaline aqueous solution of crude 2,6-NDCA in the presence of a metal catalyst such as palladium, platinum, nickel, or ruthenium at a temperature below 220°C, carbon dioxide or sulfur dioxide gas is blown into the 2,6-NDCA solution.
- A method for separating NDCA as a monoalkaline salt (Japanese Patent Application Laid-Open No. 160248/1983).

A method of dissolving crude 2,6-NDCA in an aqueous sodium acetate solution and then concentrating and crystallizing it to separate the monoalkali salt of 2,6-NDCA (Japanese Patent Application Laid-Open No. 1989-
105639).

In both methods, 2,6-NDCA is dissolved in an alkaline aqueous solution, the pH is adjusted, and the 2,6-NDCA is dissolved in an alkaline aqueous solution.
This is a method that combines a method of precipitating and purifying monoalkaline salt crystals with a heat treatment method or an oxidation-reduction treatment method.

However, by adjusting the PH mentioned above, 2,6-
The method for purifying NDCA is to use a relatively high concentration of 2,
6-This is a method in which carbon dioxide or sulfur dioxide gas is injected under pressure while heating an alkaline aqueous solution of NDCA, or mineral acid is added to adjust the pH to 6.5 to 7.5, and then the monoalkali salt is precipitated by cooling to 20°C. Therefore, due to the delicate equilibrium relationship between monoalkali salts and dialkali salts and 2,6-NDCA, there is a drawback that the crystal composition and precipitation amount are not constant depending on conditions such as pH, temperature, and concentration.

In addition, since other carboxylic acids with PKa close to 2,6-NDCA are contained in 2,6-NDCA obtained by oxidizing 2,6-dialkylnaphthalene, 2,6-NDCA can be used only by adjusting the pH. It is difficult to purify 6-NDCA to high purity. Furthermore, after separating the precipitated monoalkali salt by adjusting the pH, it is necessary to remove the mother liquor attached to and contained in the crystals by washing with water, but since the monoalkali salt of 2,6-NDCA is water-soluble, , by washing 2,6-
The disadvantage is that the yield of NDCA decreases.

Problems to be solved by the invention Purification by crystallization of monoalkali salts alone cannot
Since it is difficult to purify 6-NDCA to high purity, it has become necessary to combine it with other methods such as heat treatment, oxidation treatment, reduction treatment, etc.

However, heat treatment requires high temperature and high pressure, and when oxidation and reduction reactions are used together, there is a problem that many new by-products are generated and become impurities, and measures to remove them are required. As such, it was incomplete.

On the other hand, 2,6-NDCA has a melting point of 300°C or higher, so it is impossible to purify it by distillation, and it is soluble in most organic solvents such as methanol, ethanol, acetone, benzene, xylene, thioxane, acetonitrile, and acetic acid. Therefore, purification by recrystallization is not possible.

As described above, an appropriate method for purifying, separating and recovering 2,6-NDCA obtained by oxidizing 2,6-dialkylnaphthalene with high purity has not been proposed.

In order to obtain highly pure 2,6-NDCA, the present inventors have conducted intensive research into a method for purifying 2,6-NDCA that does not require chemical reactions, concentration, cooling, etc. Crude 2,6-NDCA obtained by oxidizing dialkylnaphthalene is mixed with an alkali selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate in an amount equal to or more than the neutralization equivalent, and the same cation as the alkali (hereinafter referred to as 2,6-
We have discovered a method for purifying 2,6-NDCA in which NDCA is precipitated as a disodium salt or a dipotassium salt, and based on this knowledge, we have accomplished the present invention.

Structure of the Invention The method of the present invention comprises washing or extracting 2,6-NDCA obtained by oxidizing 2,6-dialkylnaphthalene with water, acetic acid, or an aqueous solution of mineral acid;
6-NDCA (hereinafter abbreviated as crude 2,6-NDCA) is dissolved in water with an alkali selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate in an amount equal to or more than the neutralization equivalent, and a common cation. In addition to the solution containing the neutral salt, 2,6-
The 2,6-
This is a method to purify NDCA. Further, an acid having the same anion as the water-soluble neutral salt is added to the mother liquor from which the precipitated 2,6-NDCA has been separated, and the pH is lowered to 3 to precipitate and separate impurities. Crude 2,6-NDCA by adding potassium oxide, sodium carbonate or potassium carbonate
2,6-
This is a method to purify NDCA.

The water-soluble neutral salt of a common cation is a water-soluble neutral salt of sodium or potassium, which dissolves at least 10% by weight, preferably at least 15% by weight in water at 20°C, for example. Examples include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and potassium nitrate.

The amount of the water-soluble neutral salt added is 10 mol/or more, preferably 5 mol/or less, as a cation concentration,
Moreover, it is below the solubility of the additive. Addition exceeding the solubility is not preferable because the additive will be mixed into the salted out crystals. Also, the cation concentration
Even if it is added at a concentration of 10 mol/or more, the salting-out effect will not increase, and the specific gravity and viscosity of the solution will increase.
Solid-liquid separation becomes difficult.

The solubility of the dialkali salt of 2,6-NDCA is
It decreases rapidly as the concentration of common cations, such as sodium ions in the case of disodium salts and potassium ions in the case of dipotassium salts, increases. For example, the solubility of 2,6-NDCA in a sodium hydroxide aqueous solution with a pH of 12 at 20°C is approximately 11% when the sodium ion concentration is 1.5 mol/, but it is 7% when the sodium ion concentration is 2.2 mol/. At 3mol/, the solubility is 1.7%,
At 4mol/, the solubility is 0.4%, and when the sodium ion concentration is 5.4mol/, the solubility further decreases to 0.2%.

To explain in detail the purification method of the present invention, 2,6
- 2,6-dialkylnaphthalene such as dimethylnaphthalene or 2,6-diisopropylnaphthalene in the presence of cobalt and/or manganese and a bromine catalyst in a solvent containing 70% or more of a lower aliphatic monocarboxylic acid such as acetic acid, from 160 to Crude 2,6- obtained by oxidation by blowing pressurized air at 250°C
NDCA, neutralizing equivalent or more of sodium hydroxide,
2,6-
Crystals of dialkali salt of NDCA precipitate.

The detailed mechanism of this salting out is not clear, but at the same time 2,6-NDCA is eluted from the surface of the added crude 2,6-NDCA crystals into the alkaline solution, due to the salting out action of the coexisting cations. It is thought that the dialkali salt of 2,6-NDCA is precipitated.

On the other hand, metals such as cobalt or manganese that are present in trace amounts are changed into hydroxides or oxides by excessive alkali, and become insolubilized. Therefore, these insolubilized substances can be easily removed by dissolving the salted-out crystals in water and then separating them.

The amount of alkali added in the salting out process should be at least the neutralization equivalent, but in order to precipitate the heavy metals contained in the crude 2,6-NDCA as hydroxides or oxides, the solution should be at a pH of 9 or higher. The pH is preferably 11 or higher, and the amount used is preferably 1.2 times or more the neutralization equivalent.

In salting out, the amount of water-soluble neutral salt added and the concentration of 2,6-NDCA can be adjusted within a wide range depending on the desired purification purity, desired recovery rate, etc. That is,
The mutual concentration is closely related to the concentration of coexisting cations, but as crude 2,6-NDCA, 50
~250g/, preferably 110-180g/ is desirable for purification operations.

The solubility of the alkali salt of 2,6-NDCA is not affected by the concentration in the salting-out process, but rather changes largely depending on the concentration of common cations, so there is no need for heating or cooling during salting-out, and there is no need to concentrate. There's no need to. The temperature of the solution during salting out is usually 20~
Since the temperature is 40°C, there is less energy loss, which is preferable even in industrial implementation.

By the above-mentioned salting-out treatment, 2,6-NDCA can be recovered as a dialkali salt (disodium salt or dipotassium salt) with a purity of 99% or more.

On the other hand, since the salting-out mother liquor obtained by separating the dialkali salt of 2,6-NDCA has dissolved impurities, a mineral acid having the same anion as the water-soluble neutral salt used during salting-out is added to this mother liquor. The pH of the mother liquor is adjusted to 3 or less, and dissolved impurities are precipitated and separated. The salt concentration and pH of the solution from which impurities have been separated and removed are adjusted, and the solution thus adjusted is mixed with crude 2,6-
Circulate to the NDCA salting out process. Due to such cyclic use of the mother liquor, replenishment of aqueous neutral salts is usually not required.

The substance precipitated from the salting-out mother liquor consists of impurities and 2,6-NDCA that was not precipitated by the salting-out process. From the substance thus precipitated, 2,6-
NDCA can also be recovered, but since the 2,6-NDCA precipitated in this step has a lower purity than crude 2,6-NDCA, crude 2,6-NDCA can be recovered.
It is preferable to purify the crude 2,6-NDCA to a purity equivalent to that of the crude 2,6-NDCA and then purify it together with the crude 2,6-NDCA by the purification method of the present invention.

The purity of the dialkali salt of 2,6-NDCA separated in the salting out process can be further improved by subjecting it to the treatment described below.

Since the dialkali salt crystals of 2,6-NDCA contain heavy metal hydroxides and/or basic carbonates due to the excessive use of alkali,
6-Dissolve dialkali salt crystals of NDCA in water,
After separating the insoluble heavy metal compounds, mineral acid is added to separate and collect the 2,6-NDCA crystals.

More preferably, an aqueous solution in which dialkali salt crystals of 2,6-NDCA are dissolved is adsorbed with activated carbon, or a heavy metal compound is removed from an aqueous solution in which dialkali salt crystals of 2,6-NDCA are dissolved and then adsorption treatment is performed with activated carbon. Coloring substances, etc. can be removed by doing this.

Activated carbon can be used in any form such as granules, granules, spheres, crushed or powdered forms, but powdered activated carbon with a large surface area works effectively.

To describe the method of activated carbon treatment specifically, activated carbon may be directly added to the aqueous solution of precipitated dialkali salt of 2,6-NDCA and stirred for at least 30 minutes. It is efficient to pass an aqueous solution of dialkali salt of 2,6-NDCA through the packed bed for adsorption treatment.
The temperature of the adsorption treatment is 5 to 100°C, preferably 10 to 100°C.
It is 30℃.

When performing adsorption treatment with activated carbon, 2,6
- Adding 1 to 3% by weight of sodium chloride to the aqueous solution of dialkali salt of NDCA enhances the adsorption capacity of activated carbon, making it possible to reduce the amount of activated carbon used.

That is, crude 2,6-
Adding NDCA to salt out, washing the obtained crystals with aqueous sodium chloride, dissolving them in water, and treating with activated carbon is an advantageous method because the amount of activated carbon consumed is reduced.

When a mineral acid is added to the adsorption-treated 2,6-NDCA dialkali salt aqueous solution, 2,6-NDCA with a purity of 99% or more can be obtained with a recovery rate of 90% or more.

Effects of the Invention According to the method of the present invention, the solubility of the dialkali salt of 2,6-NDCA is reduced to about 0.2% by increasing the concentration of common cations, so there is no need for any heating concentration operation. ,6-
High purity crystals of dialkali salt of 2,6-NDCA can be obtained without increasing the concentration of impurities in the alkaline solution of NDCA.

In addition, the dialkali salt of 2,6-NDCA is poorly soluble in aqueous solutions of water-soluble neutral salts of common cations, so it is possible to wash the salted-out crystals using a solution with an appropriate salt concentration. Moreover, since dissolved impurities can be easily removed from the salting-out mother liquor and the washing solution by adding mineral acid, they can be recycled and do not require replenishment of water-soluble neutral salts.

Further, according to the method of the present invention, 2,6-NDCA of sufficient quality as an industrial raw material, that is, a purity of 99% or more, can be recovered by a single salting-out treatment. In addition, when particularly high quality 2,6-NDCA is required, colorless 2,6-NDCA with a purity of 99.8% or higher can be obtained by combining adsorption treatment with activated carbon.
NDCA can be recovered.

The recovery rate of 2,6-NDCA by the method of the present invention is usually 90% or more.

Hereinafter, the purification method of the present invention will be specifically explained with reference to Examples, but the present invention is not limited only to these Examples.

The purity of 2,6-NDCA was determined using high-performance liquid chromatography, and the bromine elemental analysis was performed using fluorescence X.
In line analysis, the colored components were found in a 25% methylamine solution.
Analyzed by OD value.

(1) High performance liquid chromatography Waters Company. Model 510 HPLC analyzer Column: Li Chrosorb-RP-8 (5 μm, Merck & Co.) and Radial Pack Cartridge C-8
(Waters) connected column Mobile phase: PH3 water/acetonitrile = 45/55
(volume ratio) solution, flow rate: 0.6 cc/min Internal standard substance: 2-naphthoic acid Detection wavelength: 260 nm (2) Fluorescence X-ray analysis method Rigaku Fluorescence X-ray analyzer (Model 3080E2) X-ray tube: Rhodium 50Kv Measured at -50mA Detector: PC detector Crystal: 10g of germanium sample is formed into a tablet with a diameter of 30mm and analyzed.

Detection limit: 3ppm (3) Analysis of colored components Dissolve 1g of sample in 10ml of 25% methylamine aqueous solution and measure the optical density using 500nm light using a 10mm quartz cell.

Example 1 2 kg of glacial acetic acid, 0.1 kg of cobalt acetate tetrahydrate, 0.2 kg of manganese acetate tetrahydrate, and odor were placed in a titanium-lined stainless steel autoclave equipped with a reflux condenser, a gas blowing tube, a temperature measuring tube, and a stirrer. Add 50g of ammonium chloride and 0.2kg of 2,6-diisopropylnaphthalene, and stir at 180-190℃.
Compressed air of 20 kg/cm ² was blown in at a rate of 600 kg/hr, and the reaction was carried out for 5 hours. After the reaction was completed, the mixture was cooled to 80°C, the precipitate was filtered, washed with hot acetic acid, 6% by weight hydrochloric acid 2 was added, and the mixture was stirred for 1 hour. After filtering and washing,
After drying, 165 g of crude 2,6-NDCA was obtained. Its purity was 94.6%, and the 25% methylamine OD value, which indicates the content of coloring components, was 0.66. Moreover, the content of bromine element was 4600 ppm. In addition, the raw material 2,6-
2,6- for diisopropylnaphthalene
The yield of NDCA was 76.7%.

20 of the crude 2,6-NDCA thus obtained
g, 8 g of sodium hydroxide, 23 g of sodium chloride
g was dissolved in 97 g of water at 25° C. with vigorous stirring, and stirring was continued for 1 hour. After the precipitated salting-out crystals were separated, they were washed with 90 g of a 19% by weight aqueous sodium chloride solution and dissolved in 300 g of water. After separating the insoluble matter, 10% by weight sulfuric acid water was added dropwise while stirring to adjust the pH of the aqueous solution to 1.5, and 2,6-NDCA was precipitated. Precipitated 2,6
-NDCA crystals were washed with water until they became neutral and then dried to obtain 18.3 g of 2,6-NDCA.

The purity of the obtained 2,6-NDCA was 99.0%, and the purity of the 25% methylamine solution, which indicates the content of coloring components, was 99.0%.
The OD value was 0.068. Also, the content of bromine element is
It was 4ppm. The recovery rate of purified 2,6-NDCA relative to crude 2,6-NDCA was 95.8%.

Example 2 20g of crude 2,6-NDCA obtained in Example 1
50g of potassium chloride and 35g of potassium carbonate and 200g of water
The mixture was added to an aqueous solution dissolved in g at 30° C. with vigorous stirring, and stirring was continued for 1 hour. After separating the precipitated salting-out crystals, add a 28% by weight aqueous potassium chloride solution.
Washed with 80g and dissolved in 500g of water. After removing insoluble matter, the liquid was passed through a bed filled with 2.3 g of powdered activated carbon for adsorption treatment. Add 10% by weight hydrochloric acid dropwise to the adsorbed aqueous solution while stirring to adjust the pH of the aqueous solution to 1.5, and add 2,6-NDCA.
was precipitated. After washing the precipitated 2,6-NDCA crystals with water until no chlorine ions were detected,
After drying, 17.6 g of 2,6-NDCA was obtained.

The purity of the 2,6-NDCA obtained was 99.8%, and the OD of the 25% methylamine solution indicates the content of coloring components.
The value was 0.018. Moreover, bromine element was not detected. In addition, purification 2 for crude 2,6-NDCA,
The recovery rate of 6-NDCA was 92.8%.

Claims (1)

[Claims] 1 Crude 2,6-naphthalene dicarboxylic acid obtained by oxidizing 2,6-dialkylnaphthalene is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate in an amount equal to or more than the neutralization equivalent. 2,6 by adding it to an aqueous solution containing the same alkali and a water-soluble neutral salt of the same cation and stirring.
2, consisting of precipitation as a disodium or dipotassium salt of naphthalene dicarboxylic acid;
A method for purifying 6-naphthalene dicarboxylic acid. 2. To the mother liquor from which the precipitated disodium salt or dipotassium salt of 2,6-naphthalene dicarboxylic acid was separated, an acid having the same anion as the water-soluble neutral salt was added to bring the pH to 3 or less, and impurities were precipitated and separated. The purification method according to claim 1, which comprises adding sodium hydroxide, potassium hydroxide, sodium carbonate, or potassium carbonate to the solution and recycling it. 3. The purification method according to claim 1, which comprises dissolving the separated dialkali salt of 2,6-naphthalene dicarboxylic acid in water and subjecting it to adsorption treatment with activated carbon. 4. The purification method according to claim 3, which comprises adding 1 to 3% by weight of sodium chloride to the solution to be subjected to adsorption treatment with activated carbon.